Empyema is a condition in which pus builds up in the pleural space, the area between the lungs and chest wall, usually as a result of a bacterial infection like pneumonia. It leads to inflammation and infection of the pleura, causing symptoms such as fever, chest pain, cough, and difficulty breathing. Empyema can develop in stages, from an initial infection to the formation of thick, fibrous pus. If untreated, it can lead to lung damage or sepsis. Treatment typically involves antibiotics, drainage of the pus, and sometimes surgery.